2) Apply the Interim patch for RU4 (KB 2581545). You will have to ring Microsoft for this (as it is not yet published) – however be warned that initially this KB number will not seem to exist. Best bet is to raise a call with the Exchange team (you will have this refunded as it is a bug/fix situation) – however I had to get to third-line Exchange guys before I got an “Yes, it’s here”. Also bear in mind that this will likely have to be removed before RU5 can be applied (when it is released).